Some notes on old units of measurement, which may be helpful when studying old maps and documents relating to land use.
Units of length
- 1 yard = 3 feet [1 yard is approximately 0.914 metres]
- 1 chain = 22 yards
- 1 chain = 100 links
- 1 rod = 1 perch = 1 pole = 25 links or 5.5 yards = 16 1/2 feet = 1/4 chain
- 1 furlong = 10 chains = 40 rods = 220 yards
- 1 mile = 8 furlongs = 80 chains
- 3 miles = 1 league
- 3 barleycorns = 1 inch
Units of area
- 1 acre = 1 chain x 1 furlong = 10 square chains = 4840 square yards
- 1 acre = 4 roods
- 1 rood = 1 furlong x 1 rod = 40 square perches or square rods = 1210 square yards
- 1 square perch = 1 square rod = 30.25 square yards
Chains and links were named for surveying methods. Most of the other units were agricultural in origin. Furlong meant furrow length. During the Middle Ages, an acre was the amount of land that could be ploughed in one day with a yoke of oxen (approximately!), and was one chain in width (22 yards), and one furlong (10 chains, or 220 yards) in length.
The land areas given in the 19th Century tithe apportionments are given in acres, roods and perches. By perches they actually meant square perches. As above, there are 40 square perches in a rood and 4 roods in an acre.
Britain’s railways are still measured in miles and chains.